Temperature compensated indicating



PatentedJuly 18,1939 j I 2,166,595.

UNITED STATES-PATENT OFFICE TEMPERATURE COMPENSATED INDICATINGINSTRUMENT Cletus J. Jenny, East Orange, N. J., assignor to BendixAviation Corporation, South Bend, 1111]., a corporation of DelawareApplication May 21, 1937, Serial No. 144,095

3 Claims. (Cl. 73-4) The present'invention relates to improvementspressly understood, however, that the drawing'is in indicatinginstruments, and more particularly for the purpose of illustration anddescription to means'for compensating the effectof'temperaonly and isnot designed as a definition of the ture upon an indicating instrumentand to cor limits of the invention, reference being had for rect oreliminate backlash'and other sources of this purpose to the appendedclaims. 5

error in such instruments.- In the drawing wherein like reference char-Instruments utilizing expansible or resilient acters refer to like partsthroughout the several elements as their actuating means are subject toviews:

various sources of error. Upon a change in tem- Fig. 1 is a sideelevation, partlyin section, of

IQ perature for instance, the modulus of elasticity one form of deviceembodying the invention; of the material used in the expanding orresilient Fig. 2 is a view taken along the line 2-2 of element changes,thereby causing error. Also Fig. 1; and upon a change in temperature thevarious e'le- Fig. 3 is a plan view of the device as shown in merits ofthe mechanism change in physical di- Fig. 1.

l5 mension thereby affecting the indication of the Referring to thedrawing wherein the inven- 5 instrument. tion is illustrated as appliedto an altimeter, the

In addition to errors due to temperature operating mechanism of thealtimeter is shown change, undesirable backlash may exist betweenmounted on a frame of any suitable type which, the various elements ofthe mechanism thereby in the present embodiment, comprises a rearreducing the precision of the instrument. This ame ber 0 Plate and aface Plate r 20 is particularly true in instruments where a high a dplates being held in Sp e relation by magnification of the forceproduced by the exp cers l2, and screws l3.

- panding or resilient element is used, such as in Mounted on bottomspacer I2 by means of holsensitive altimetem low rod 14 and screw 15, asshown in Fig. 2, is

26 In addition to the difiiculties enumerated above, diaphragm the lowerSide' Of which has a it rod l8 attached thereto and passing throughhollow rod It in which itflis lockedin place by screw l5. Adjustablymountedin center post IS on the other side of said diaphragm is rod 20to which is pivoted one end of link 2| by pin 22. Screw 3o 23 fastenstherod 20 in place after it has been properly adjusted. Rotatably connectedto the other end of link 2| by means of threaded pin 24 and nuts 25 (seeFig. 1) is a bi-metal element 26 which is adjustably mounted onrockshaft 21 by a means of rod 28 slidably mounted in said rockshaft andlocked in adjusted position therein by screw'29.

Bi-metal element 26 is constructed of two different metals in a mannerwell known in the art 0 the plane of whose mounting surfaces is normalhigh precision instruments are also subject to vibration whereby anoscillation of the indicating element occurs and other undesirableresults ensue.

30 Accordingly, one of the objects of the 'present invention is toprovide novel means in an indicating or measuring instrument whereby theforegoing undesirable characteristics are eliminated.

A further object is to provide novel means in an indicating or measuringinstrument whereby errors due to changes in physical dimensions withchanges in temperature are compensated.

Still a further object is to provide novel means whereby backlash iseliminated.

40 A still further object is to provide novel means zi gffig zgz ii gg2: :2 are reduced to the axis of rod 28 while the e ds of said bimetalelement 18 parallel to the axls of rockshaft 1 Still another oblect isto provide a novel means Upon expansiun and contraction of the .1: forproducing i h effect the metal element the effective lever arm betweencompensating force is apphed tangentially to an the link 2| and the rkshaft 2 is varied element whereby the lever arm of the force is wchanges in temperature; the modulus f maintained substantially constantupon relative elasticity f the diaphragm or other expanding movement ofthe elements of the mstl'umentor resilient element changes. This changeis in- 1 The a ve and furth r j ts and advantages dicated by acoefficient called the temperature 5 0f t invention w pp r fullyhereinafcoeflicient of the modulus of elasticity. Upon a ,ter from aconsideration of the detailed descripchange in the modulus ofelasticity, for 'a given tion whichfollows, taken together with theacincrement in pressure a different increment of companyingdrawingwherein is illustrated one expansion of the diaphragm or resilientelement embodiment of the invention. It is to be exis produced atdifferent temperatures. In order to compensate for this change thebi-metal element is designed so that such change in expansion of'thediaphragm will be compensated bends towards the rockshaft with adecrease in temperature thereby reducing the lever arm between saidbi-metal element and said rockshaft. By the reduction of said lever armthe point of application of the force due to the expanding diaphragm,namely, the upper end of link 2|,

travels in a circular path of smaller radius whose center is the centerof the rockshaft. A smaller expansion of diaphragm l6, therefore, ischanged to an increased angular rotation of rockshaft 21 and suchincreased angular rotation is transmitted to the pointer therebyoffsetting the reduced movement of the pointer due to the lesserexpansion of the diaphragm at said lower temperature. The bi-metalelement 26 is mounted on the slidable rod 28 so that the initial leverarm between the bi-metal element and the rockshaft can be accuratelyadjusted thereby'enabling the adjustment of said lever arm to' providemeans whereby the most effective compensation can be produced, withoutinjury to the bi-metal strip 26 or any impairment. of the functionsthereof,

Rockshaft 21 is mounted for rotation by extensions thereof, one of whichis-journaled in boss 30 formed on back plate l and the other of which isjournaled in front plate ll.

Mounted on rockshaft 21 adjacentrod 28 is, sector gear 3| meshingwithpinion 32 mounted for rotation with shaft 33 carrying pointer 34 atone end thereof. Shaft 33 is journaled at one end in plate 34a mountedon front plate II by spacers 35 and screws 36 and is journaled adjacentits other end in front plate H.

The novel means of the invention are now provided and for this purposethere is attached to shaft 33 a collar 31 to which is fastened one endof a small spiral spring 38 the other end of which is connected to oneof the spacers 35 as shown spring 39 is connected tangentially to saidcollar 40 whereby the effective lever arm of the force exerted by thespring on the rockshaft is maintained substantially constant regardlessof the angular rotation of said rockshaft. By this tangential connectionthe torque exerted by the spring 39 is made constant throughout therange of the instrument. The spiral spring can be set to give positiveor negative torque, but no change from positive to negative torque. Thusthe link 2| is constantly under tension or compression but does notchange from one to the other whether the instrument is going from itszero reading to the maximum reading or back from the maximum reading tothe zero reading.- There is, therefore, no lost motion in the pin jointsof the link and readings going up the scale all correspond to readingscoming down the scale. The application of the spring force tangentiallyto the collar maintains this torque constant throughout the entire rangeof the instrument. I

Spiral spring 39 is connected to the frame of the instrument by beingfastened to one of theupper spacers l2 through screw 42. Due to the factthat the spiral spring is so attached and by exerting a load on thediaphragm l6, oscillation due to vibration is greatly reduced and thisreduction is made throughout the range of the instrument.

The small spiral spring 38 is attached to collar 31 in the same manneras spring 39 is connected to collar 40 and therefore exerts a constanttorque on the shaft 33 throughout the range of the instrument andmaintains the same surfaces of the teeth of the pinion 32 and sectorgear 3| in contact thereby eliminating backlash between the rockshaftand pointer and further reducing vibration throughout the, range of theinstrument.

In the present embodiment, the spiral spring 39 is constructed ofsuitable bi-metal whereby it is possible to compensate for any shifts ofzero reading due to temperature effects. At a so that the torque willincrease or decrease by desired amounts with an increase in temperature.If an increase in temperature changes the physical dimensions of theelements of the operating mechanism so that the indication of thepointer has a plus error the bi-metallic spiral spring is so designedthat the change in torque at the increase of temperature will change theload exerted on the diaphragm in such a manner and in such magnitudethat an equal negative error will be introduced. This nullifles theerror due to the temperatureefiect.

The operation of the device is as follows! When the diaphragm element l6expands due for instance to a decrease in pressure on the outsidethereof, link 2! is moved upwardly to actuate the bi-metal element 26 tothereby rotate rockshaft 21. The effective lever arm between the bimetalelement and the rockshaft is varied by temperature changes therebyoffsetting changes in the expansion of the diaphragm [6 due to changesin temperature affecting its modulus of elasticity. Changes in thephysical dimensions of the elements of the operating mechanism due tochanges in temperature or, in other words, the zero compensation, iseffected by changes in torque of the 'bi-metal spiral spring 39.Bi-metal spring 39 also applies a uniform torque to the rockshaft where-.by the elements between said rockshaft and the diaphragm are eitherunder tension or compres-. sion and all backlash is eliminated. Also theload placed by the spiral spring 39 on the diaphragm and its connectionbetween the movable and stationary parts of the instrument reducevibration of the movable elements and the attachmerit of the spring 39tangentially to the,

collar 40 applies a uniform torque throughout the 7s range ofthe-instrument. The movement transmitted to the rockshaft rotates thesector gear 3| thereby rotating pinion 32 and shaft 33 to rotate thepointer 34. Small spiral spring 38 prevents backlash between the pointerand the rockshaft, reduces vibrationand by means of its attachment tocollar 31, applies a corrective torque of constant value throughout therange of the instrument.

Means are therefore provided whereby errors due to temperature arecompensated, backlash and oscillation due to vibration are reduced, the

most efiicient setting for proper compensation can be accuratelydetermined and set and the corrective forces made constant throughoutthe range of the instrument.

Although but one embodiment of the invention has been illustrated a anddescribed, further changes and modifications in form, materials andrelative arrangement of parts, which will now appear to those skilled inthe art, may be made without departing from the scope of the invention.Reference is, therefore, to be had to the appended claims for adefinition of the limits of the invention.

What is claimed is: 1. In a precision indicating device, a frame work,an expansible element mounted insaid" framework, a rockshaft, meansconnectingsaid expansible elementto said rockshaft, an indicatingelement, means connecting said indicating element to said rockshaft, abi-metal spiral spring tangentially connected at one end thereof to saidrockshaft and to the framework at the other end thereof,-and a secondcoil spring having one end connected to said framework and the other endto said connecting means between said indicating element and saidrockshaft.

2. In a precision indicating device, an expansible element, anindicating element, means including a rockshaft transmitting the motionof said expansible element to said indicating element, and meanscomprising'a bi-metal spiral spring independent of the motiontransmitting means, with one end thereof fixedly secured and the otherend connected to said rockshaft and applying a torque to said rockshaft,constant for all positions of said rockshaft and varying only .withtemperature whereby temperature errors in said indicating device areproperly compensated. 3. In a device of the character described, anexpansible element, a rock-shaft connected to said expansible element, abi-metallic spiral spring having one end thereof' tangentially connectedto said rock-shaft for rotation therewith, the other end of said springbeing immovably held, an indicating element and means trans- 'mittingthe rotation of sai rock-shaft to said indicating element.- 1

CLE'I'US J. JENNY.

